InlineLevelBox position is relative to the parent inline box. LineBox converts it to relative to the line box.
Created attachment 412855 [details] Patch
Created attachment 412857 [details] Patch
Committed r269231: <https://trac.webkit.org/changeset/269231> All reviewed patches have been landed. Closing bug and clearing flags on attachment 412857 [details].
<rdar://problem/70926149>